The present invention relates to a method of monitoring a circuit or an apparatus and, more particularly, to a method of monitoring stand-by circuits (apparatuses) which are installed in equipment having a redundant configuration.
Communication equipment or similar equipment which has to be extremely reliable is provided with a stand-by circuit which replaces an active circuit when the active circuit fails. Such equipment is also provided with a monitor for constantly monitoring the stand-by circuit, so that the stand-by circuit may function normally in the event that the active circuit is replaced. Typically, a dummy signal or a similar monitoring signal is fed to the stand-by circuit so as to determine whether the circuit is normally operable on the basis of the resultant output signal of the circuit. It has been customary to provide a monitor of the type using such a monitoring method with monitoring signal generating circuits and monitoring signal receiving circuits, each being associated with a particular stand-by circuit.
The conventional monitor as stated above has a problem left unsolved. Specifically, in the case of an apparatus for multiplexing communication channels, for example, the number of monitoring signal generating circuits and the number of receiving circuits needed are the same as the number of channels. This increases the overall dimensions, cost, and power consumption of the monitor.